Apparatus for the electrolysis of alkali metal chloride solutions with mercury cathode

ABSTRACT

AN APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE SOLUTIONS WITH MERCURY CATHODE. FRESH BRINE IS DELIVERED THROUGH A HOLLOW SHAFT AND UNIFORMLY DISTRIBUTED TO A PLURALITY OF PASSAGES IN THE ANODE. SMALL OPENINGS IN THE PASSAGES ON THE ACTIVE SIDE OF THE ANODE ENABLE BRINE TO PASS INTO THE NARROW ELCTROLYSIS GAP BETWEEN THE ANODE AND MERCURY CATHODE. SMALL OPENINGS IN THE SOLID PART OF THE ANODE OR BETWEEN THE PASSAGES ENABLE THE WEAKENED BRINE CHARGED WITH SMALL CHLORINE GAS BUBBLES TO FLOW INTO THE CELL CHAMBER.

March 5, 1974 F. GLOS ETAL 3,795,603

APPARATUS FOR THE ELECTROLYSIS 0F ALKALI METAL CHLORIDE SOLUTIONS WITH MERCURY CATHODE Original Filed Aug. 26, 1971 6 Sheets-Sheet l March 5, 1974 F. GLOs ETAL 3,795,603 APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE SOLUTIONS WITH MERCURY CATHODE Original Filed Aug. 26, 1971 6 Sheets-Sheet 2 Fig.2

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ALKALI METAL APPARATUS FOR THE ELECTROLYSIS OF CHLORIDE SOLUTIONS WITH MERCURY CATHODE Original Filed Aug. 26, 1971 6 Sheets-Sheet 5 O 0 O O 0 0 O O O O 0 0 GOO-00000000000 March 5, 1974 GLOS EI'AL 3,7955603 APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE SOLUTIONS WITH MERCURY CATHODE 6 Sheets-Sheet 4 Original Filed Aug. 26, 1971 m mm mm r March 5, 1974 F. GLOS ETAL 3,795,603

APPARATUS FOR THE ELECTROLYSIS OF ALKALI METAL CHLORIDE SOLUTIONS WITH MERCURY CATHODE Original Filed Aug. 26, 1971 6 Sheets-Sheet 5 F. GLOS ET 3, 795,603

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March 5, 1974 APPARATUS FOR THE ELECTROLYSIS 0F ALKALI METAL CHLORIDE SOLUTIONS WITH MERCURY CATHODE Original Filed Aug. 26, 1971 NJ I mm mm United States Patent US. Cl. 204219 Claims ABSTRACT OF THE DISCLOSURE An apparatus for the electrolysis of alkali metal chloride solutions with mercury cathode. Fresh brine is delivered through a hollow shaft and uniformly distributed to a plurality of passages in the anode. Small openings in the passages on the active side of the anode enable brine to pass into the narrow electrolysis gap between the anode and mercury cathode. Small openings in the solid part of the anode or between the passages enable the weakened brine charged with small chlorine gas bubbles to flow into the cell chamber.

CROSS-REFERENCE TO RELATED APPLICATION This is a division of application, Ser. No. 175,066, filed Aug. 26, 1971, now US. Pat. No. 3,746,631.

BACKGROUND OF THE INVENTION In the electrolysis of an alkali metal chloride solution with utilization of a mercury cathode, the aim is to decrease the costs of an electrolysis installation in this way, that the current density is increased and the floor space of the electrolytic cell is held as small as possible. By means of high cathodic current density, the loss as a result of reduction of the chlorine formed on the anode and the re-formation of alkali chloride is lessened and thereby the electrolytic efliciency is improved.

High electric current density has as a result a high gas production speed per surface entity of the active anode surface. The bubbles of chlorine gas then become so small that their diameter amounts to less than 0.1 mm. and their rising speed lies in the Stokes range. The lift or buoyancy of the gas bubbles then is no longer sufficient to remove the bubbles from the anode surface. The small gas bubbles are very stable and combine with difficulty into larger bubbles. They remain dispersed in the electrolytes, are by means of local circulation of the brine entrained or pulled along again into the intermediary space of the anode and the cathode and form together with the newly occurring gas a foam which prevents the passage or flow of current by means of its insulating effect and causes in this way an increase in the cell tension and a greater expenditure of energy.

It has been suggested that in order to facilitate the movement of the gas bubbles away from the active anode surface, inclined cathode and anode surfaces and/or grooved and perforated anode plates may be employed.

By means of coarse perforation of the anode plates, as for example suggested in the US. Pat. No. 3,308,043, probably for larger gas bubbles, the ascending path may be shortened. However, an appreciable part of the active anode surface is lost in this manner.

By means of the differentiated structureof the active Patented Mar. 5, 1974 ICC anode surface, there results a non-uniform current distribution. The very small gas bubbles, which occur with a particularly high current density and contribute to the formation of foam have, however, an ascending speed so small that through a construction of this type, no essential advantage is achieved.

SUMMARY OF THE INVENTION The object of this invention is to produce an apparatus through which, with similar cell size, a larger output of cells is secured. The increase in the current density required for the purpose with similar or smaller cell tension may be attained in the most effective way by means of a change in the flow conditions in the reaction chamber between anode and cathode. The apparatus is characterized in that fresh brine is conveyed to the area of each individual anode plate and is uniformly distributed over the active anode surface facing the reaction chamber.

An apparatus is produced which is characterized by at least one hollow anode shaft per anode, which is connected with numerous cavities disposed in the anode plate, the walls of said cavities having on the active side of the anode plate numerous small openings. Through the hollow shaft of the anode fresh brine is supplied and is distributed in the cavities of the anode plate over the entire anode surface, and then passes out through numerous small holes in the active anode surface into the reaction chamber between anode and cathode.

In order that not all gas bubbles forming in the reaction chamber must travel over a large part of the active anode surface up to the edge of the anode plate for escaping from the reaction chamber, it is of advantage to provide the anode at the non-hollow places in the anode plate likewise with numerous small holes, through which gas bubbles may escape before the fresh brine subsequently flows into the upper cell chamber.

The direct feed of the fresh brine into the reaction chamber and the short path for the formed gas bubbles insure the energizing of the electrolysis cell according to the invention wtih high current density at low voltage drop, so that the electrolytic efiiciency is substantially increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional elevation of an electrolysis cell showing a reaction chamber containing a mercury cathode and an anode plate, the foam from the chamber being degasified in a separator which is diagrammatically shown;

FIG. 2 is a vertical sectional view of the anode plate assembly taken on the line 2-2 of FIG. 3;

FIG. 3 is a top plan view of the anode plate assembly shown in FIG. 1;

FIG. 4 is a vertical sectional view of an alternate form of anode plate assembly in which both the top and bottom plate members are profiled and taken on the line 4-4 of FIG. 5;

FIG. 5 is a fragmentary top plan view of an alternate form of anode plate assembly shown in FIG. 4;

FIG. 6 is a fragmentary bottom plan view of the anode plate shown in FIG .5;

FIG. 7 is a vertical sectional view on the line 77 of FIG. 8 of an alternate form of anode plate assembly in which the pipes are flatened on the underside, the upper side being dome-shaped in cross section;

FIG. 8 is a fragmentary top plan view of the form shown on FIG. 7;

FIG. 9 is a sectional view substantially on the line 9-9 of FIG. 8;

FIG. 10 is a vertical sectional view on the line 1010 of FIG. 11 showing an alternate form of anode plate assembly in which the pipes are rectangular in cross section;

FIG. 11 is a fragmentary top plan view of the form shown on FIG. 10;

FIG. 12 is a sectional view substantially on the line 1212 of FIG. 11;

FIG. 13 is a vertical sectional view on the line 13--13 of FIG. 14 showing an alternate form somewhat similar to that shown on FIGS. 10 to 12 but in which current is supplied to the anode plate through guide rails;

FIG. 14 is a fragmentary top plan view of the form shown in FIG. 13; and

FIG. 1 is a sectional view of the guide rails and a rectangular pipe, the parts connected to the upper rail being removed.

DESCRIPTION OF PREFERRED EMBODIMENTS The electrolysis installation is shown diagrammatically by way of example in FIG. 1. Fresh brine supplied to the anode within a closed chamber 4a through a centrally disposed tube 1 made of titanium, distributes itself at the foot radially into the cavities 2 of the anode plate and enters through the bores 3 into the narrow electrolysis gap between anode and the mercury cathode within the chamber 4a. The weakened brine flows out charged with small chlorine gas bubbles through bores 4 into the cell chamber. This foam leaves the cell through tuyeres 5 and is degasified in a separator 6 by means of dropwise addition of diluted hydrochloric acid at 9. The anolyte flows through feed pipes 7 downwardly and the chlorine gas escapes upwardly through feed pipes 8.

In order to distribute the fresh brine for an entire cell uniformly in the individual anodes, each anode brine feed has connected in front a nozzle 11. The current is supplied through a copper tube 10, which is protected on the outside by a pipe made of titanium or a temperature and chlorine resistant synthetic material. The mercury flows in direction of the rows of holes in the anode plate, the brine flowing transversely to this direction.

The anode consists of metal, preferably of titanium, whose active surface is covered with a coating layer protecting against passivation and amalgamation. The inner surfaces of the anode cavities must likewise be passivated. All bores and slots in the anodes are rounded off on the lower side in order to prevent an increased current density at these points, which may have as a result a destruction or corrosion of the protective covering layer. The hollow anode plate not only affords good brine distribution, but also a good current distribution without noteworthy decrease in voltage, which would cause a non-uniform current density.

Prerequisite for the utilization of the method according to the invention is a large quantity of brine with reference to a correspondingly high brine speed in the dissociation or decomposition chamber between anode and cathode for washing away the gas bubbles and for the formation of a foam with flow tendency. The progress must be with low weakening, that is, instead of 35 grams per liter according to the conventional method, with a weakening of approximately 5 grams per liter with a specific load of 30 ka./ m9. Per cm. anode surface and seconds there result according to Faraday 0.00106 gram of chlorine gas, which corresponds with moist chlorine of approximately 75 C. to a volume of 0.59 cmfi/second. For 1 ton of chlorine there was required 1.7 ton NaCl so that with 5 g./l. weakening 0.36 cm. brine/ sec. anode surface are required. The mixture flowing out of the anode amounts then to 0.59 plus 0.36:0.95 cm. /sec. cm. The portion of gas in the foam is accordingly 62%. The specific weight of the foam amounts accordingly to even 0.46 kp./l. as compared with about 1.2 kp. of the brine. With an electrode gap of about 0.5 mm. a brine speed sets in, in the dissociation chamber of about 0.3 m./sec.

A form of anode structure is shown on FIGS. 2 and 3 in which a rigid, level plate 14 made of titanium is welded to a profiled pressed titanium plate 15. The rim is continuously welded and in the grooves the upper plate 15 is joined at the points of bores 4 with the lower plate 14 by means of spot welding. In the center of the plate is seated a tuyere 16 made of titanium, which is connected with a pipe 1 by screwthreads of welding. Its outer circumference carries threads, on which a copper pipe 10 is screwed for the current feed. The pipe 10 is protected on the outside against attack by moist chlorine by means of a casing 17. Between the plate 15 and the pipe 10 is disposed a packing 18, which is tightened by means of the screwed on copper pipe 10.

In the center of the anode plate below the anode shaft the bores 4 cannot be disposed in the same arrangement. The bores 4 disposed next to the center must be dimensioned somewhat larger in diameter, so that the bubbles developed in the center may pass with the brine into the upper cell chamber.

FIGS. 4 to 6 show an anode construction with pressed plates 19 and 20 of titanium profiled on both sides, which are welded together at the rim. At the points of the bores 4 the plates 19 and 20 are connected in the grooves 22 by means of spot welding. The groove shaped depressions on the lower side of the anode plate are continuous, while the depressions on the upper side, in the center and through the brine distribution strips 21 lying transversely to the direction of mercury flow are interrupted. This construction has the advantage that the continuous depressions in the center bring about a better carrying away of the foam.

FIGS. 7, 8 and 9 show a further anode construction, which is composed of pipes 23 made of titanium rounded at their upper sides and flattened on their lower side 5. The pipes are connected in the center with a pipe 24' having a transversely disposed brine and current distribution pipe part 24. For good brine distribution to all pipes, the inlet openings 23' disposed in the center on the pipes are made so small that they act as nozzle. The pipes 23 are inserted in and welded to curved recesses ,26 in the distribution pipe part 24. The pipe 24 has a cover plate 25 welded or soldered to the pipe part 24. The brine foam may escape from the reaction chamber through gaps 26 between the pipes in the upper cell chamber. Holes or bores 3 in the flat side of each pipe 23 enables brine to flow to the gap between the anode and mercury cathode.

FIGS. 10 to 12, as well as FIGS. 13 to 15, show similar anode constructions, only with the difference, that instead of the flattened pipes 23, rectangular pipes 27 are utilized. With the anode according to FIGS. 13 to 15, the current is supplied to the anode plate through current guide rails 28 and 29. By means of this arrangement of rails, a still better current distribution is secured over the anode surface.

What we claim is:

1. Apparatus for the electrolysis of alkali metal chloride solution in which a reaction chamber is arranged between an anode and a mercury cathode, said apparatus comprising an anode structure in the form of a series of parallel closely arranged pipes, opposite ends of which are closed, there being gaps between adjacent pipes to enable the escape of brine foam, a closed ended pipe extending transversely across said series of pipes, each of the pipes of said series having an aperture opening into said transverse pipe and an aperture opposite thereto to permit the outlet of fresh brine to the gap between the anode and mercury cathode, an upstanding tube through which fresh brine is introduced to said transverse pipe, and an electrically conductive pipe outside of said tube and through which electric current is delivered to said anode structure.

2. Apparatus as claimed in claim 1, in which the sides of the pipes in said parallel series facing the mercury cathode are flattened.

3. Apparatus as claimed in claim 2, in which the upper sides of the pipes in said parallel series are outwardly rounded.

4. Apparatus as claimed in claim 1, in which said apertures in said pipe series are so small as to act as nozzles.

5. Apparatus as claimed in claim 1, in which said transverse pipe is disposed centrally of said series of pipes.

6. Apparatus as claimed in claim 1, in which each of the pipes in said parallel series are rectangular in cross section.

7. Apparatus as claimed in claim 6, in which said transverse pipe is at one end portion of said pipe series, a similar transverse pipe at the other end portion of said pipe series, pipe means connecting said transverse pipes,

electric current passing from said electrically conductive pipe through said connecting pipe means and transverse pipes to said pipe series.

References Cited UNITED STATES PATENTS 3,409,519 11/1968 Gallone et al 204219 X 3,507,771 4/1970 Donges et al 204-284 3,535,223 10/1970 Baecklund et al. 204284 X JOHN H. MACK, Primary Examiner I D. R. VALENTINE, Assistant Examiner US. Cl. X.R. 204250, 284 

